Group health care plans (what your employer gives you) are given largely without consideration for the health of the individuals involved. Basic tests, like making sure you don't have a major heart problem and pee tests are involved but thats it. Friends of mine who have a business with only 3 employees listed me as one of their employees to get the number up to four. Some how I was registered whilst living in another country.

And I believe there are already laws on the books about pre-existing conditions (assuming you have continuous coverage)